The present invention relates to an intake structure of an internal combustion engine.
There is known a technique in which a tumble flow swirling along an axis direction of a cylinder chamber is formed by intake air in order to perform combustion of an internal combustion engine efficiently.
In that case, an intake port is provided to be inclined to one side of a cylinder chamber with respect to the center line of the cylinder chamber, so as to form the tumble flow.
In order to improve the efficiency of the combustion of the internal combustion engine, it is important to obtain a strong tumble flow stably.
In JP-U-H7-25235, it is proposed that a protrusion part which generates a deflection flow for generating a tumble flow is provided in the intake port, and the protrusion part is formed of an elastic bellows.
According to JP-U-H7-25235, the strength of the deflection flow is adjusted by adjusting the swelling amount of the protrusion part, so that the strength of the tumble flow is adjusted according to the load of the internal combustion engine.
In JP-A-2004-316609, it is proposed that a stepped part which projects to the inside of the intake port is provided in a boundary between a wall surface positioned on the far side from the one side of wall surfaces of the intake port and a throat part of a valve seat continuous to the intake port.
According to JP-A-2004-316609, the flow of the intake air guided along the wall surface positioned on the far side from the one side of the wall surfaces of the intake port, that is, the intake air in a direction opposite to the tumble flow is disturbed by the stepped part. The flow rate of the intake air guided in the cylinder chamber on the side opposite to the one side, that is, the intake air in the direction opposite to the tumble flow is controlled to obtain a strong tumble flow.
However, in the related art, it is not considered how to prevent the partial backflow of the tumble flow formed in the cylinder chamber to the intake port.
Particularly, when the internal combustion engine is operated with a high expansion ratio, in a case where the intake valve is closed late at the timing when a piston rises from a bottom dead center to a top dead center, the fuel-air mixture in the cylinder chamber more easily flows back to the intake port as the tumble flow is stronger. For this reason, there is a concern that a charging efficiency is deteriorated. In addition, generally, a cylinder head forms the valve seat or the like in a casting by machining. However, for example, in a case where the stepped part is formed by using the machine processing, there is a concern that the position of the stepped part is varied according to a processing accuracy, and the variation occurs to the height of the stepped part when a deviation of a mold at the time of casting is repeated.
The invention has been made in consideration of the above situation, and an object thereof is to provide an intake structure of an internal combustion engine which is advantageous for strengthening a tumble flow in a cylinder chamber and preventing a backflow of a fuel-air mixture to an intake port.